When the room in question presents vertical walls of profile that is irregular, either because of a local projection or setback, or because of the presence of a portion that is curved in convex or concave manner, it is no longer possible to make do with measurements performed in ordinary manner of the three or four rectilinear sides in question for the purpose of subsequently cutting out the work surface that is to be put into place. Thus, when there are irregularities of greater or lesser size in the horizontal profile line in question, use is made of templates of card or plywood with the edge of such a template being progressively shaped by hand so as to fit as closely as possible to the horizontal profile line defined by the vertical walls in question.
In order to avoid the need to make temporary templates, proposals have also been made to use an interferometer for measuring the corners of a room with a laser beam, however accuracy is then of the order of five millimeters which is not very satisfactory, while also being very limiting as to the shape of the irregularities concerned.
Finally, proposals have also been made to use three-dimensional measuring arms of the kind that are conventionally used in building cars or airplanes, but although such arms provide relatively satisfactory accuracy, they are extremely expensive, and not always easy to put into place on the site where the measurements are to be made.
The state of the art is also illustrated by various article positioning devices, such as plotters. U.S. Pat. No. 4,412,383, and U.S. Pat. No. 4,583,292 illustrate cable driven plotters. A more sophisticated device is illustrated in U.S. Pat. No. 4,918,817 which discloses an apparatus using tapes which are pushed or pulled by associated-drive means responsive to signals from control means, said tapes having sufficient stiffness to resist bending under compressive loads applied by the tape drive means in order to be able to pull or push the article over a work surface.